Ink composition and ink set

ABSTRACT

It is an object of the present invention to reduce uneven glossiness of images formed with pigmented ink compositions on glossy inkjet media by setting the type of surfactant and the content of an alkanediol and a glycol ether. The ink composition of the present invention contains a pigment, an alkanediol, a glycol ether, a polyether-modified polysiloxane compound, a water-soluble organic solvent, and water, and the sum of the contents of alkanediol and glycol ether is 10 wt % or more, but less than 20 wt %.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink composition, particularly to anink composition that results in a good glossiness on glossy media andsolves the problem of uneven glossiness by reducing the differences inglossiness between the colors, and an ink set having such inkcomposition.

2. Description of Prior Art

An inkjet recording method is a method of printing by jetting drops ofan ink composition onto a recording medium such as paper. A feature ofthis method is that high-resolution and high-quality images can beprinted at high speed using a relatively inexpensive apparatus. Inkcompositions commonly used in the inkjet recording method typicallycontain water as their main ingredient, mixed together with coloringcomponents and wetting agents such as glycerin to prevent clogging. Dyeinks and pigmented inks can be used as colorants. However for printedmatter, since pigmented inks are superior to dye inks in terms ofweathering resistance such as light fastness, water fastness and gasfastness, the demand for pigmented inks is increasing. Therefore, thedevelopment of pigmented inks in which the characteristics of pigmentsare utilized, has been in progress.

With recent innovative improvements in inkjet recording technology, theinkjet recording method has been applied in the field of high-definitionprinting that had already been achieved with the silver halide photoprinting method and the offset printing method. Accordingly,developments have also been made in the area of inkjet recording mediawhere high glossiness comparable to photographic paper and art paperwhich are used in the silver halide photo printing method and the offsetprinting method, has been achieved. As for high-glossy recording mediafor inkjet printing, the mainstream is a substrate (e.g., paper, film,etc.) having thereon an ink-absorbing layer that contains porousmaterial such as porous silica.

When forming color images using the inkjet recording method, inkcompositions of three colors, yellow, magenta, and cyan, are used, or insome cases, four colors including a black ink composition. There arealso cases where a light cyan ink composition and a light magenta inkcomposition are added to the four ink compositions listed above, so thatcolor images are formed by using six colors. When printing to arecording medium using a plurality of color ink compositions, if therespective ink compositions have widely differing ink penetrations(i.e., ink absorption speeds) into the recording medium, the printedimages usually suffer from bleeding, uneven colors, uneven flocculation,and uneven glossiness, thus the quality of the recorded images isreduced.

Compared to dye inks, pigmented inks in which pigments serve ascolorants are more prone to uneven flocculation, since the pigments arelayered on the surface of a recording medium.

According to the definition in Patent Laid-Open Publication No.2002-138232, color unevenness refers to the unevenness in the imagequality when overlapping colors as secondary and tertiary colors due tothe ink components having different absorption speeds, respectively.Uneven flocculation refers to image ruoughness (graininess) when dots ofdifferent colors overlap each other due to the respective ink componentshaving different absorption speeds. Uneven glossiness refers to thedifferences in glossiness due to the differences in absorption speedsbetween the respective ink components.

As a solution for these problems, the same patent teaches that, in anink set having multiple pigmented ink compositions, the absorptioncoefficients of the respective ink compositions are limited within apredetermined range, so that uneven colors, uneven flocculation, anduneven glossiness are reduced. The absorption coefficients are indicatedin the testing method approved by the Japan Technical Association of thePulp and Paper Industry, that is, “Bristow's method” (JAPAN TAPPI No.51)(for example, see page 350 of Shin Kami no Kagaku (New Science of Paper)4th edition, co-written by Takashi Kadoya et al.).

The same patent discloses an ink composition containing, as apenetrating agent, an acetylene glycol compound and a polyhydric alcoholalkyl ether derivative having three or more carbons.

A number of pigmented ink compositions using pigments as colorants havebeen proposed, one of which is the ink composition disclosed in PatentLaid-Open Publication No. 2001-354889, that exhibits adequatepenetration and ink discharge stability by containing glycol ether and1,2-alkandiol.

Patent Laid-Open Publication No. H11-349871 discloses an ink compositioncontaining a colorant, an aqueous carrier, an alkanediol having hydroxygroups at the each terminal, a polyethylene glycol with a molecularweight of about 200 to 5000, a mixture of polyethylene glycol andpolypropylene glycol, and a polyol/polyalkylene oxide condensate havinga specified structure. These patents show that the respective inkcompositions provide an excellent optical density for printed matter andgood printing properties for inkjet printers.

However, these ink compositions still have room for improvement inrelation to the glossiness of images when printed on glossy media havingink-absorbing layers. Therefore, it is desired that an ink compositionthat exhibits excellent glossiness on glossy inkjet media should bedeveloped.

SUMMARY

The present invention was made to solve the problems of the prior art.It is an object of the present invention to provide an ink compositionand an ink set including such ink composition, where it is possible toform images having reduced uneven glossiness on glossy inkjet media.

After rigorous research, the inventor of the present inventiondiscovered that it is possible to form images with reduced unevenglossiness on glossy inkjet media by using a polyether-modifiedpolysiloxane compound as a surfactant to be contained in the inkcomposition, and by setting the alkanediol content and the glycol ethercontent and the weight ratio thereof.

The present invention is based on such discovery, and provides an inkcomposition containing a pigment, an alkanediol, a glycol ether, apolyether-modified polysiloxane compound, a water-soluble organicsolvent, and water, wherein the sum of the contents of alkanediol andglycol ether is 10 wt % or more, but less than 20 wt %.

By obtaining the ink composition as above, it is possible to form imageshaving high glossiness and reduced uneven glossiness on the glossyinkjet media.

The present invention also provides an ink set including the inkcompositions. By using such ink set, it is possible to reduce glossdifferences between colors of the respective ink compositions in the inkset, and to prevent uneven glossiness.

The present invention further provides a recording method for printingby making an ink composition adhered onto a recording medium, and theabove ink compositions are used in this recording method.

Since the ink compositions obtained as above are used in this recordingmethod, it is possible to form print images having high glossiness andreduced uneven glossiness between colors, even when glossy inkjet mediais used.

The present invention further provides an ink-jet recording method forprinting by jetting drops of an ink composition onto a recording medium,and any of the aforementioned ink compositions is used in this ink-jetrecording method.

Since the ink compositions obtained as above are used in this inkjetrecording method, it is possible to form print images having reduceduneven glossiness between colors, even when glossy inkjet media is used.

The ink compositions of the present invention ensure that the imagesprinted on glossy inkjet media have high glossiness and reduced unevenglossiness. Examples of the recording methods where the ink compositionsof the present invention are used include recording methods in whichwriting instruments (e.g., pens) are used; the inkjet recording method;and various other printing methods. Among these methods, the recordingmethod of the present invention is preferably used in the ink-jetrecording method, in which drops of the ink compositions are jetted andmade adhered to the recording medium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The ink composition of the present invention contains a polyethermodified polysiloxane compound as a surfactant. To enhance glossiness,it is preferable to use, for example, a polyether modifiedorganosiloxane compound represented by the following formula, as thepolyether modified polysiloxane used in this ink composition.

(In this formula, each of R¹ to R⁷ independently represents a C₁₋₆ alkylgroup; each of g, j, and k independently represents an integer numberequal to 1 or greater; EO represents an ethyleneoxy group; PO representsa propyleneoxy group; p and q are both integer numbers equal to 0 orgreater but the sum of p and q is an integer number equal to 1 orgreater; and EO and PO may be random or block, with the order thereof inthe brackets [ ] being irrelevant.)

Regarding the polyether modified organosiloxane compound expressed bythe general formula (1), it is preferable that each of R¹ to R⁷independently represents an alkyl group, more preferably a methyl grouphaving 1 to 6 carbons. Each of g, j, and k, independently represents aninteger number equal to 1 or greater, preferably integer numbers 1 to 2.P and q are integer numbers equal to 0 or more, but the sum of p and qis an integer number equal to 1 or greater, preferably an integer number2 to 4.

As the compound expressed by the general formula (1), it is preferableto use, for example, a compound that satisfies j=k+g. It is alsopreferable to use a compound in which each of R¹ to R⁷ is a methylgroup, j is 2, k is 1, g is 1, p is an integer number equal to 1 orgreater, and q is 0.

Compounds that can be expressed by the general formula (1) arecommercially available and it is possible to use such compounds. Forexample, silicon surfactants, BYK-345, BYK-346, BYK-347, or BYK-348 (allavailable from BYK-Chemie Japan) may be used.

The amount of the polyether-modified polysiloxane compound added to theink composition may be appropriately selected, but it is preferable forthe amount to be in a range of 0.03 to 3 wt %, more preferably 0.1 to 2wt %, and most preferably 0.3 to 1 wt % relative to the ink composition.

The ink composition of the present invention contains alkanediol,preferably 1,2-alkanediol. As for the 1,2-alkanediol, 1,2-alkanediolhaving 4 to 6 carbons, for example, 1,2-butanediol, 1,2-pentanediol, or1,2-hexanediol is preferably used in terms of enhancing glossiness andpreventing bleeding.

In a preferred embodiment of the present invention, to enhance thestability for the dispersion of the pigment in the ink composition, the1,2-alkanediol is selected from the group consisting of 1,2-butanediol,1,2-pentanediol, and 1,2-hexanediol.

In a more preferred embodiment of the present invention, the1,2-alkanediol is preferably 1,2-hexanediol or 1,2-pentanediol. It ismost preferable that 1,2-hexanediol should be used. In the presentinvention, these substances may either be used alone or two or more ofthem can be used together.

The amount of alkanediol added to the ink composition is selectedconsidering the amount of glycol ether added to the ink, which will bedescribed later. However, it is preferable for the amount to be in therange of 3 to 20 wt %, more preferably of 4 to 18 wt %, and mostpreferably of 5 to 15 wt % relative to the ink composition.

In the ink composition of the present invention, a glycol ether is used.Examples of the glycol ether include ethylene glycol monomethyl ether,ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,ethylene glycol monomethyl ether acetate, diethylene glycol monomethylether, diethylene glycol monoethyl ether, diethylene glycolmono-n-propyl ether, ethylene glycol mono-iso-propyl ether, diethyleneglycol mono-iso-propyl ether, ethylene glycol mono-n-butyl ether,ethylene glycol mono-t-butyl ether, diethylene glycol mono-n-butylether; triethylene glycol mono-n-butyl ether; diethylene glycolmono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycolmonomethyl ether, propylene glycol monoethyl ether, propylene glycolmono-t-butyl ether, propylene glycol mono-n-propyl ether, propyleneglycol mono-iso-propyl ether, propylene glycol mono-n-butyl ether,dipropylene glycol mono-n-butyl ether, dipropylene glycol monomethylether, dipropylene glycol monoethyl ether, dipropylene glycolmono-n-propyl ether, and dipropylene glycol-iso-propyl ether.

In a preferred embodiment of the present invention, it is preferablethat, among these glycol ethers, a polyhydric alcohol alkyl ether shouldbe used. In particular, in terms of ink penetration, it is preferable touse ethylene glycol monoethyl ether, ethylene glycol monobutyl ether,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobutyl ether, triethylene glycol monomethyl ether,triethylene glycol monoethyl ether, or triethylene glycol monobutylether. Among these, it is most preferable to use triethylene glycolmonobutyl ether.

The amount the glycol ether added to the ink composition is determinedconsidering the added amount alkanediol which was described earlier.However, it is preferable for the amount to be in the range of 1 to 20wt %, more preferably of 2 to 15 wt %, and most preferably of 3 to 10 wt% relative to the ink composition.

When the total weight of the ink composition is set as a reference (100wt %), the sum of the contents of alkanediol and glycol ether is 10 wt %or more but less than 20 wt %.

By setting the alkanediol content and the glycol ether content, it ispossible to reduce the differences in glossiness between colors.Consequently, the uneven glossiness of images printed on glossy mediacan be reduced.

If it is desired to enhance only the gloss levels of the images, inkcompositions can be prepared by simply combining alkanediol and thepolyether modified polysiloxane compound. However, when such inkcompositions are used in an ink set, the gloss differences between thecolors become evident, making uneven glossiness even more apparent. But,if ink compositions are prepared by combining an alkanediol, a glycolether, and a polyether-modified polysiloxane compound, the glossdifferences between the colors are reduced, and uneven glossiness isreduced.

When the sum of the contents of alkanediol and glycol ether is less than10 wt %, the gloss levels will decrease. However, when the sum exceeds20 wt %, the viscosity of the ink composition increases, making itinappropriate for such ink composition to be used in an inkjet printer.

The weight ratio of the alkanediol and the glycol ether(alkanediol/glycol ether) is in the range of 0.7 to 4, preferably in therange of 0.8 to 2.5, and most preferably in the range of 1.0 to 1.5.

Since the reflection intensity of each color changes according to theweight ratio of the alkanediol and the glycol ether, if the weight ratiois set as above, the gloss differences between the colors can be madesmaller and the uneven glossiness can be reduced.

The colorant used in the present invention is a pigment. It is notnecessary to limit the types of pigment to obtain the effects of thepresent invention, and any inorganic or organic pigment can be used.

As inorganic pigments, it is possible to use, in addition to titaniumoxide and iron oxide, carbon black which is manufactured using apublicly known method such as the contact method, the furnace method orthe thermal method.

Examples of organic pigments include: azo pigments such as insoluble azopigments, condensed azo pigments, azo lake, and chelated azo pigments;polycyclic pigments such as phthalocyanine pigments, perylene pigments,perinone pigments, anthraquinone pigments, quinacridone pigments,dioxazine pigments, thioindigo pigments, isoindolinone pigments, andquinophthalone pigments; dye chelates (e.g. basic dye chelates, acid dyechelates etc.); nitro pigments; nitroso pigments; aniline black; andfluorescent pigments. Each can either be used alone or in a plurality,mixed together.

Examples of the pigment used as carbon black include the following: No.2300, No. 900, HCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100,No. 2200B and other pigments manufactured by Mitsubishi ChemicalCorporation; Raven 5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255,Raven 700 and other pigments manufactured by Columbian ChemicalsCompany; Regal 400R, Regal 330R, Regal 660R, Mogul L, Mogul 700, Monarch800, Monarch 880, Monarch 900, Monarch 1000, Monarch 1100, Monarch 1300,Monarch 1400 and other pigments manufactured by Cabot Corporation; andColor Black FW1, Color Black FW2V, Color Black FW18, Color Black FW200,Color Black S150, Color Black S160, Color Black S170, Printex 35,Printex U, Printex V, Printex 140U, Special Black 6, Special Black 5,Special Black 4A, Special Black 4 and other pigments which aremanufactured by Degussa Corporation. Each can be used either alone or ina plurality mixed together.

As to the pigment used for a yellow ink composition, it is preferable touse one or more pigments selected from the group consisting of C.I.pigment yellows 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95, 97,98, 109, 110, 114, 128, 129, 138, 150, 151, 154, 155, 180, and 185. Outof these, it is particularly preferable to use one or more selected fromthe group consisting of C.I pigment yellows 74, 109, 110, 128, and 138.

As to the pigment used for a magenta ink composition and a light magentaink composition, it is preferable to use one or more pigments selectedfrom the group consisting of C.I. pigment reds 5, 7, 12, 48 (Ca), 48(Mn), 57 (Ca), 15:1, 112, 122, 123, 168, 184, 202, 209, and C.I. pigmentviolet 19. Out of these, it is particularly preferable to use one ormore pigments selected from the group consisting of C. I. pigment reds122, 202, 209, and C.I. pigment violet 19.

As to the pigment used for a cyan ink composition and a light cyan inkcomposition, it is preferable to use one or more pigments selected fromthe group consisting of C.I. pigment blues 1, 2, 3, 15:3, 15:4, 15:34,16, 22, and 60, and C.I. vat blues 4 and 60. Out of these, it isparticularly preferable to use one or more pigments selected from thegroup consisting of C.I. pigments blue 15:3, 15:4, and 60.

As to the pigment used for an orange ink composition, it is preferableto use one or more pigments selected from the group consisting of C.I.pigment oranges 5, 36, 43, and 62.

As to the pigment used for a red ink composition, it is preferable touse one or more pigments selected from the group consisting of C.I.pigment reds 17, 49:2, 112, 149, 177, 178, 188, 255, and 264. Out ofthese, it is particularly preferable to use one or more pigmentsselected from the group consisting of C.I. pigment reds 149, 177, 178,and 264.

As to the pigment used for a blue ink composition, it is preferable touse C.I. pigment blue 60.

As to the pigment used for a violet ink composition, it is preferable touse one or more pigments selected from the group consisting of C.I.pigment violets 3, 19, 23, 32, 36, and 38. Out of these, it isparticularly preferable to use C. I. pigment violets 19 or 23, or both.

As to the pigment used for a green ink composition, it is preferable touse one or more pigments selected from the group consisting of C.I.pigment greens 1, 4, 7, 8, 10, 17, 18, and 36.

In a preferred embodiment of the present invention, it is preferable touse a pigment having a mean particle diameter of 50 to 200 nm. Theamount of pigment added may be appropriately selected to the extent thatan adequate image density can be achieved. However, it is preferable forthe amount to be 0.5 to 15 wt % relative to the ink composition.

The pigment content (in terms of solids) used in the present inventionmay be appropriately selected, but it is preferable for the amount to be3 wt % or less, and more preferably in a range of 1 to 3 wt %, relativeto the ink composition.

In a preferred embodiment of the present invention, in terms of thedispersion stability of the pigment in the ink composition, the inkcomposition further contains a dispersion resin for dispersing thepigment in the ink composition. It is preferable for the pigment of thepresent invention to be added to the ink in the form of apigment-dispersed liquid obtained by dispersing the pigment in awater-based solvent using the dispersion resin.

As a dispersant preferable for the ink composition of the presentinvention, it is possible to use a dispersant that is commonly used inthe preparation of pigment-dispersed liquids, for example, amacromolecular dispersant.

As to the preferable macromolecular dispersant for the ink compositionof the present invention, natural macromolecules may be used, forexample, proteins such as glue, gelatin, casein, and albumin; naturalrubber such as gum arabic and tragacanth gum; glucosides such assaponin; alginic acid derivatives such as alginic acid, alginic acidpropyleneglycol ester, triethanolamine alginate, and ammonium alginate;and cellulose derivatives such as methylcellulose,carboxymethylcellulose, hydroxyethylcellulose, andethylhydroxyethylcellulose.

Moreover, synthetic macromolecules may also be used as the preferablemacromolecular dispersant. Examples of synthetic macromolecules include:acrylic copolymers such as polyvinylalcohols, polyvinylpyrolidones,polyacrylic acid, acrylic acid-acrylonitrile copolymer, potassiumacrylate-acrylonitrile copolymer, vinyl acetate-acrylate estercopolymer, and acrylic acid-alkyl acrylate ester copolymer;styrene-acrylic acid resins such as styrene-acrylic acid copolymer,styrene-methacrylic acid copolymer, styrene-methacrylic acid-acrylicalkyl ester copolymer, stryene-alpha-methylstyrene-acrylic acidcopolymer, and stryene-alpha-methylstyrene-acrylic acid-acrylic alkylester copolymer; styrene-maleic acid; styrene-maleic anhydride;vinylnaphthalene-acrylic acid copolymer; vinylnaphthalene-maleic acidcopolymer; and vinyl acetate copolymers such as vinyl acetate-ethylenecopolymer, vinyl acetate-fatty acid vinyl ester-ethylene copolymer,vinyl acetate-maleic acid ester copolymer, vinyl acetate-crotonic acidcopolymer, and vinyl acetate-acrylic acid copolymer; and the saltsthereof.

Among the above, particularly preferable are: macromolecular compoundshaving carboxyl groups (preferably in the form of salts) (e.g.,styrene-acrylic acid resins, styrene-maleic acid resin, styrene-maleicanhydride resin, vinylnaphthalene-acrylic acid copolymer,vinylnaphthalene-maleic acid copolymer, and vinyl acetate-acrylic acidcopolymer); copolymers formed from monomers having a hydrophobic groupand monomers having a hydrophilic group; and polymers formed frommonomers having both a hydrophobic group and hydrophilic group in theirmolecular structures.

Examples of the salts include diethylamine, ammonia, ethylamine,triethylamine, propylamine, isopropylamine, dipropylamine, butylamine,isobutylamine, triethanolamine, diethanolamine, aminomethylpropanol, andmorpholine. The average molecular weight of these (co)polymers ispreferably 3,000 to 30,000, and more preferably 5,000 to 15,000.

The amount of the dispersion resin added may be appropriately selected,but is preferably 0.5 to 5 wt %, and more preferably 1 to 3 wt %relative to the ink composition.

The ink composition of the present invention contains water and awater-soluble organic solvent. Examples of the water-soluble organicsolvent of the present invention include glycerin, ethylene glycol,diethylene glycol, triethylene glycol, tetraethylene glycol; propyleneglycol, dipropylene glycol, tripropylene glycol, polyethylene glycolwith its molecular weight being 2,000 or less, 1,3-propylene glycol,isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol,1,5-pentaediol, 1,6-hexanediol, meso-erythritol, and pentaerythritol.Among these, it is preferable for glycerin to be used.

These water-soluble organic solvents preferably enhance the solubilityof other contained components into the ink composition, improvepenetration of the ink into a recording medium such as paper, andeffectively prevent nozzle clogging.

The amount of the water-soluble organic solvent added to the inkcomposition may be appropriately selected, but it is preferable for theamount to be about 1 to 30 wt %, and more preferably, about 5 to 15 wt %relative to the ink composition.

The ink composition of the present invention may further contain nozzleanti-clogging agents, preservatives, antioxidants, electricalconductivity adjusting agents, pH regulators, viscosity adjustingagents, surface tension adjusting agents, and oxygen absorbents.

Examples of the preservatives or fungicides include: sodium benzonate;sodium pentachlorophenol; 2-pyridine thiol-1-oxide; sodium sorbate;sodium dehydroacetate; and 1,2-dibenzine thiazoline-3-one (Proxel CRL,Proxel BND, Proxel GXL, Proxel XL-2, and Proxel TN, all are availablefrom Avecia Limited).

Examples of the pH regulators, dissolution accelerators or antioxidantsinclude amines and transformations thereof such as diethanolamine,triethanolamine, propanolamine, and morpholine; inorganic salts such aspotassium hydroxide, sodium hydroxide, and lithium hydroxide; ammoniumhydroxide; quaternary ammonium hydroxide (tetramethylammonium, etc.);carbonates such as potassium carbonate, sodium carbonate, and lithiumcarbonate; phosphates; ureas such as N-methyl-2-pyrrolidone, urea,thiourea, and tetramethylurea; alohanates such as alohanate and methylalohanate; biurets such as biuret, dimethyl buiret, tetramethyl biuret;and L-ascorbic acid, and salt thereof.

The ink composition of the present invention may contain antioxidantsand UV absorbing agents, for example, Tinuvin 328, 900, 1130, 384, 292,123, 144, 622, 770 and 292 available from Ciba-Geigy Japan Limited;Irgacor 252 and 153; Irganox 1010, 1076 and 1035; MD1024; and lanthanideoxides.

The ink composition of the present invention may be prepared, forexample, by dispersing and mixing the aforementioned componentsaccording to an appropriate method. At first, a pigment, a dispersant,and water are preferably mixed using an appropriate disperser (e.g.,ball mill, sandmill, atrighter, roll mill, agitator mill, Henshellmixer, colloid mill, supersonic homogenizer, jet mill, ong mill) andmade into a homogeneous pigment-dispersed liquid. At the same time,components other than the pigment and the dispersant are mixed and madeinto an ink solvent. The obtained pigment-dispersed liquid is drippedinto this ink solvent while being agitated. Optionally, saccharides, pHregulators, preservatives, fungicides and other agents may be added anddissolved thoroughly into the ink solution. After fully being agitated,the ink solution is filtered to remove large coarse particles andforeign matter which can cause clogging. Thus, an ink composition isobtained.

The present invention provides a recording method for printing by makingthe ink composition adhered onto a recording medium, wherein theaforementioned ink composition is used.

Since the ink composition obtained as above is used in the recordingmethod of the present invention, when a glossy inkjet medium is used, itis possible to form print images having good glossiness and reduceduneven glossiness between the colors.

Moreover, the present invention provides recorded matter formed usingthe aforementioned ink composition.

Since the recorded matter of the present invention is formed using theink compositions obtained as above, even when a glossy inkjet medium isused, it is possible to form print images having reduced unevenglossiness between the colors.

Examples of the recorded matter of the present invention includerecorded matter having print images in which uneven glossiness isreduced even when printed on the glossy ink-jet medium.

EXAMPLES

The present invention is now explained in detail referring to thefollowing examples. These examples, however, shall not limit the scopeof the present invention.

<Ink Preparation>

A pigment, a styrene-acrylic acid copolymer as a dispersant, and waterwere thoroughly mixed, and this mixture was dispersed in a sand mill(manufactured by Yasukawa Seisakusyo) together with glass beads(diameter=1.7 mm; 1.5 times the weight of the mixture) for two hours.After dispersion, the glass beads were removed, and a pigment-dispersedliquid was obtained.

In addition to the obtained pigment-dispersed liquid, components otherthan the pigment and the dispersant were mixed and made into an inksolvent. This ink solvent was dripped gradually into thepigment-dispersed liquid and this mixture was thoroughly stirred fortwenty minutes at room temperature. Then, the mixture was filtered byusing a membrane filter having a pore size of 5 μm. Finally, an inkcomposition was obtained.

Example 1 Ink Set 1

Cyan ink composition C.I. pigment blue 15:3 2.0 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   8 wt % Triethyleneglycol monobutyl ether  10 wt % Diethylene glycol  10 wt % BYK 348(manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange water RemainderMagenta ink composition C.I. pigment red 122 2.0 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   8 wt % Triethyleneglycol monobutyl ether  10 wt % Glycerin   5 wt % Diethylene glycol   5wt % BYK 348 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchangewater Remainder Yellow ink composition C.I. pigment yellow 74 3.0 wt %Styrene-acrylic acid copolymer (dispersant)   1 wt % 1,2-hexanediol   8wt % Triethylene glycol monobutyl ether  10 wt % Glycerin   8 wt % BYK348 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange waterRemainder Black ink composition Carbon black MA 7 (manufactured byMitsubishi Chemical 2.0 wt % Corporation) Styrene-acrylic acid copolymer(dispersant)   1 wt % 1,2-hexanediol   8 wt % Triethylene glycolmonobutyl ether  10 wt % Glycerin  10 wt % BYK 348 (manufactured byBYK-Chemie Japan) 0.3 wt % Ion-exchange water Remainder

Example 2 Ink Set 2

Cyan ink composition C.I. pigment blue 15:3 3.0 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol 7.5 wt % Diethyleneglycol monobutyl ether   3 wt % Diethylene glycol  10 wt % BYK 347(manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange water RemainderMagenta ink composition C.I. pigment red 122 3.0 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol 7.5 wt % Diethyleneglycol monobutyl ether   3 wt % Glycerin   5 wt % Diethylene glycol   5wt % BYK 347 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchangewater Remainder Yellow ink composition C.I. pigment yellow 74 3.0 wt %Styrene-acrylic acid copolymer (dispersant)   1 wt % 1,2-hexanediol 7.5wt % Diethylene glycol monobutyl ether   3 wt % Glycerin   8 wt % BYK347 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange waterRemainder Black ink composition Carbon black MA 7 (manufactured byMitsubishi Chemical 2.0 wt % Corporation) Styrene-acrylic acid copolymer(dispersant)   1 wt % 1,2-hexanediol 7.5 wt % Diethylene glycolmonobutyl ether   3 wt % Glycerin  10 wt % BYK 347 (manufactured byBYK-Chemie Japan) 0.3 wt % Ion-exchange water Remainder

Example 3 Ink Set 3

Cyan ink composition C.I. pigment blue 15:3 1.5 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   5 wt % Triethyleneglycol monobutyl ether   5 wt % Diethylene glycol  10 wt % BYK 348(manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange water RemainderMagenta ink composition C.I. pigment violet 19 2.0 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   5 wt % Triethyleneglycol monobutyl ether   5 wt % Glycerin   5 wt % Diethylene glycol   5wt % BYK 348 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchangewater Remainder Yellow ink composition C.I. pigment yellow 74 3.0 wt %Styrene-acrylic acid copolymer (dispersant)   1 wt % 1,2-hexanediol   5wt % Triethylene glycol monobutyl ether   5 wt % Glycerin   8 wt % BYK348 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange waterRemainder Black ink composition Carbon black MA 7 (manufactured byMitsubishi Chemical 1.5 wt % Corporation) Styrene-acrylic acid copolymer(dispersant)   1 wt % 1,2-hexanediol   5 wt % Triethylene glycolmonobutyl ether   5 wt % Glycerin  10 wt % BYK 348 (manufactured byBYK-Chemie Japan) 0.3 wt % Ion-exchange water Remainder

Example 4 Ink Set 4

Cyan ink composition C.I. pigment blue 15:3   2 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   7 wt % Diethyleneglycol monobutyl ether  10 wt % Diethylene glycol  10 wt % BYK 348(manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange water RemainderMagenta ink composition C.I. pigment red 122   2 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   7 wt % Diethyleneglycol monobutyl ether  10 wt % Glycerin   5 wt % Diethylene glycol   5wt % BYK 348 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchangewater Remainder Yellow ink composition C.I. pigment yellow 74 3.0 wt %Styrene-acrylic acid copolymer (dispersant)   1 wt % 1,2-hexanediol   7wt % Diethylene glycol monobutyl ether  10 wt % Glycerin   8 wt % BYK348 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange waterRemainder Black ink composition Carbon black MA 7 (manufactured byMitsubishi Chemical 2.0 wt % Corporation) Styrene-acrylic acid copolymer(dispersant)   1 wt % 1,2-hexanediol   7 wt % Diethylene glycolmonobutyl ether  10 wt % Glycerin  10 wt % BYK 348 (manufactured byBYK-Chemie Japan) 0.3 wt % Ion-exchange water Remainder

Example 5 Ink Set 5

Cyan ink composition C.I. pigment blue 15:3   2 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   8 wt % Triethyleneglycol monobutyl ether   2 wt % Diethylene glycol  10 wt % BYK 348(manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange water RemainderMagenta ink composition C.I. pigment red 122   2 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   8 wt % Triethyleneglycol monobutyl ether   2 wt % Glycerin   5 wt % Diethylene glycol   5wt % BYK 348 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchangewater Remainder Yellow ink composition C.I. pigment yellow 74 3.0 wt %Styrene-acrylic acid copolymer (dispersant)   1 wt % 1,2-hexanediol   8wt % Triethylene glycol monobutyl ether   2 wt % Glycerin   8 wt % BYK348 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange waterRemainder Black ink composition Carbon black MA 7 (manufactured byMitsubishi Chemical 2.0 wt % Corporation) Styrene-acrylic acid copolymer(dispersant)   1 wt % 1,2-hexanediol   8 wt % Triethylene glycolmonobutyl ether   2 wt % Glycerin  10 wt % BYK 348 (manufactured byBYK-Chemie Japan) 0.3 wt % Ion-exchange water Remainder

Comparative Example 1 Ink Set 6

Cyan ink composition C.I. pigment blue 15:3 2.0 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   8 wt % Triethyleneglycol monobutyl ether  10 wt % Diethylene glycol  10 wt % E-1010 0.3 wt% Ion-exchange water Remainder Magenta ink composition C.I. pigment red122 2.0 wt % Styrene-acrylic acid copolymer (dispersant)   1 wt %1,2-hexanediol   8 wt % Triethylene glycol monobutyl ether  10 wt %Glycerin   5 wt % Diethylene glycol   5 wt % E-1010 0.3 wt %Ion-exchange water Remainder Yellow ink composition C.I. pigment yellow74 3.0 wt % Styrene-acrylic acid copolymer (dispersant)   1 wt %1,2-hexanediol   8 wt % Triethylene glycol monobutyl ether  10 wt %Glycerin   8 wt % E-1010 0.3 wt % Ion-exchange water Remainder Black inkcomposition Carbon black MA 7 (manufactured by Mitsubishi Chemical 2.0wt % Corporation) Styrene-acrylic acid copolymer (dispersant)   1 wt %1,2-hexanediol   8 wt % Triethylene glycol monobutyl ether  10 wt %Glycerin  10 wt % E-1010 0.3 wt % Ion-exchange water Remainder

Comparative Example 2 Ink Set 7

Cyan ink composition C.I. pigment blue 15:3   2 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   4 wt % Triethyleneglycol monobutyl ether   4 wt % Diethylene glycol  10 wt % BYK 348(manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange water RemainderMagenta ink composition C.I. pigment red 122   2 wt % Styrene-acrylicacid copolymer (dispersant)   1 wt % 1,2-hexanediol   4 wt % Triethyleneglycol monobutyl ether   4 wt % Glycerin   5 wt % Diethylene glycol   5wt % BYK 348 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchangewater Remainder Yellow ink composition C.I. pigment yellow 74 3.0 wt %Styrene-acrylic acid copolymer (dispersant)   1 wt % 1,2-hexanediol   4wt % Triethylene glycol monobutyl ether   4 wt % Glycerin   8 wt % BYK348 (manufactured by BYK-Chemie Japan) 0.3 wt % Ion-exchange waterRemainder Black ink composition Carbon black MA 7 (manufactured byMitsubishi Chemical 2.0 wt % Corporation) Styrene-acrylic acid copolymer(dispersant)   1 wt % 1,2-hexanediol   4 wt % Triethylene glycolmonobutyl ether   4 wt % Glycerin  10 wt % BYK 348 (manufactured byBYK-Chemie Japan) 0.3 wt % Ion-exchange water Remainder[Evaluation 1: Gloss Evaluation]

The above ink sets were loaded into a PM-4000 PX ink-jet printer(manufactured by Seiko Epson Corporation) to print an image of a figure(SCID sample of the Japanese Standards Association JIS X 9201-1995) onPM photo paper. The glossiness of each printed image was evaluatedvisually.

-   A: When a fluorescent light was shone on the printed side of the    paper, the light was clearly reflected.-   B: When a fluorescent light was shone on the printed side of the    paper, the clarity of the reflected light was slightly low.-   C: When a fluorescent light was shone on the printed side of the    paper, the reflected light was dull and the clarity was poor.    [Evaluation 2: Uneven Glossiness Evaluation]

After printing under the same printing conditions as above, the unevenglossiness of the respective printed images were evaluated visually.

-   AA: High-quality glossiness was achieved evenly on the printed side    of paper.-   A: Glossiness was achieved evenly on the printed side of paper,    resulting in good printing.-   B: Some uneven glossiness occurred on the printed side of paper.-   C: Severe uneven glossiness occurred on the printed side of paper,    and interference of light (iridescent light) occurred.

Evaluation results were as follows. Indicated in the table belowtogether with the evaluation results are the surfactants used, the sumof the contents of alkanediol (1) and glycol ether (2) in the inkcompositions ([(1)+(2)]), and the weight ratio ([(1)/(2)]).

TABLE 1 (1)/ Examples Surfactant (1) + (2) (2) Evaluation 1 Evaluation 2Example 1 BYK 347   18 wt % 0.8 A AA Example 2 BYK 347 10.5 wt % 2.5 AAA Example 3 BYK 347   10 wt % 1.0 A AA Example 4 BYK 348   17 wt % 0.7A A Example 5 BYK 348   12 wt % 4.0 A A Comparative E-1010   18 wt % 0.8C C Example 1 Comparative BYK 348   8 wt % 1.0 B C Example 2

1. An ink composition comprising: a pigment; a dispersion resin fordispersing the pigment; at least one alkanediol; a glycol ether; apolyether-modified polysiloxane compound; a water-soluble organicsolvent; and water, wherein the sum of all alkanediol and glycol etherin the ink composition is 10 wt % or more, but less than 20 wt %.
 2. Theink composition according to claim 1, wherein a weight ratio ofalkanediol to glycol ether is in a range of 0.7 to
 4. 3. The inkcomposition according to claim 1, wherein the polyether modifiedpolysiloxane compound is a polyether modified organosiloxane compoundrepresented in the following formula

wherein each of R¹ to R⁷ independently represents a C₁₋₆ alkyl group;each of g, j, and k independently represents an integer number equal to1 or greater; EO represents an ethyleneoxy group; PO represents apropyleneoxy group; p and q are both integer numbers equal to 0 orgreater but the sum of p and q is an integer number equal to 1 orgreater; and EO and PO may be random or block, regardless of the orderin the square brackets [ ].
 4. The ink composition according to claim 1,wherein the at least one alkandiol is selected from the group consistingof 1,2-butanediol, 1,2-pentadiol, and 1,2-hexanediol.
 5. The inkcomposition according to claim 1, wherein the glycol ether comprises apolyhydric alcohol alkyl ether.
 6. The ink composition according toclaim 5, wherein the polyhydric alcohol alkyl ether is selected from thegroup consisting of ethylene glycol monoethyl ether, ethylene glycolmonobutyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, diethylene glycol monobutyl ether, triethylene glycolmonomethyl ether, triethylene glycol monoethyl ether, and triethyleneglycol monobutyl ether.
 7. The ink composition according to claim 1,wherein the concentration of the pigment contained in the inkcomposition is 3.0 wt % or less in terms of solids.
 8. An ink setcomprising the ink composition according to claim
 1. 9. A recordingmethod for printing comprising (a) providing the ink compositionaccording to claim 1, and (b) making the ink composition adhere to arecording medium.
 10. An inkjet recording method for printing by jettingdrops of an ink composition onto a recording medium, wherein the inkcomposition according to claim 1 is used as the ink composition for thismethod.
 11. A recorded matter recorded by the recording method accordingto claim 9.